Astronomy Chapter 17 Answers – Flashcards
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critical density
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the value of the mass density of the universe that, ignoring any cosmological constant, is just barely capable of halting expansion of the universe
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cosmological constant
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A constant, introduced into general relativity by Einstein, that characterizes an extra, repulsive force in the universe due to the vacuum of space itself
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dark energy
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A form of energy that permeates all of space (including the vacuum) producing a repulsive force that accelerates the expansion of the universe
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flatness problem
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The surprising result that the sum of (omega)mass plus (omega)(upside-down carrot?) is extremely close to unity in the present day universe; equivalent to saying that it is surprising the universe is so close to being exactly flat.
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Heisenberg uncertainty principle
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The physical limitation that the product of the position and the momentum of a particle cannot be smaller than a well-defined value, Planck's constant
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horizon problem
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The puzzling observation that the cosmic background radiation is so uniform in all directions, despite the fact that widely separated regions should have been "over the horizon" from each other in the early universe
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inflation
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An extremely brief phase of ultra-rapid expansion of the very early universe. Following this, the standard Big Bang models of expansion apply
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electromagnetic force
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The force, including both electric and magnetic forces, that acts on electrically charged particles. One of four fundamental forces of nature
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strong nuclear force
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The attractive short-range force between protons and neutrons that holds atomic nuclei together; one of the four fundamental forces of nature, mediated by the exchange of gluons
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weak nuclear force
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The force underlying some forms of radioactivity and certain interactions between subatomic particles. It is responsible for radioactive beta decay and for the intial proton-proton interactions that lead to nuclear fusion in the Sun and other stars. One of the four fundamental forces of nature, mediated by the exchange of W and Z particles
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gravity
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1. the mutually attractive force between massive objects 2. An effect arising from the bending of spacetime by massive objects 3. One of four fundamental forces of nature
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quantum electrodynamics (QED)
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The quantum theory describing the electromagnetic force and its mediation by photons
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electroweak theory
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The quantum theory that combines descriptions of both the electromagnetic force and the weak nuclear force
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quantum chromogynamics (QCD)
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The quantum mechanical theory describing the strong nuclear force and its mediation by gluons
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quark
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The building block of protons and neutrons
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gluon
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The particle that carries (or, equivalently, mediates) interactions due to the strong nuclear force
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standard model
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The theory of particle physics that combines electroweak theory with quantum chromodynamics to describe the structure of known forms of matter
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antiparticle
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An elementary particle of antimatter identical in mass but opposite in charge and all other properties to its corresponding ordinary matter particle
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pair production
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The creation of a particle-antiparticle pair from a source of electromagnetic energy
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grand unified theory (GUT)
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A unified quantum theory that combines the strong nuclear, weak nuclear, and electromagnetic forces but does not include gravity
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Planck era
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The early time, just after the Big Bang, when the universe as a whole must be described with quantum mechanics
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theory of everything (TOE)
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A theory that unifies all four fundamental forces of nature: strong nuclear, weak nuclear, electromagnetic, and gravitational forces
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string theory
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The theory that conceives of particles as strings in 10 dimensions of space and time; the current contender for a theory of everything
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hierarchical clustering
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The "bottom-up" process of forming large-scale structure. Small-scale structure first produces groups of galaxies, which in turn form clusters, which then form superclusters
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cold dark matter
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Particles of dark matter that move slowly enough to be gravitationally bound even in the smallest galaxies
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axion
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A hypothetical elementary particle first proposed to explain certain properties of the neutron and now considered a candidate for cold dark matter
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photino
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An elementary particle related to the photon. One of the leading candidates for cold dark matter
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hot dark matter
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Particles of dark matter that move so fast that gravity cannot confine them to the volume occupied by a galaxy's normal luminous matter
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multiverse
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A collection of parallel universes that together comprise all that is
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eternal inflation
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The idea that a universe might inflate forever. In such a universe, quantum effects could randomly cause regions to slow their expansion, eventually stop inflating, and experience an explosion resembling our Big Bang
